giovedì 24 dicembre 2009
Pituitary stalk interruption syndrome (PSIS)
Figure 1: Coronal T1-weighted non-contrast of the pituitary gland demonstrates complete absence of the anterior pituitary gland. The posterior pituitary gland is ectopic in location.
Figure 2: Sagittal T1-weighted noncontrast of the pituitary gland demonstrates complete absence of the anterior pituitary gland. The posterior pituitary gland is ectopic in location.
Figure 3: Contrast enhanced sagittal T1-weighted of the sella turcica demonstrates complete absence of anterior pituitary gland, truncated pituitary stalk and ectopic posterior pituitary gland.
Diagnosis: Pituitary stalk interruption (PSIS) syndrome
Pituitary stalk interruption syndrome, also known as pituitary stalk transection syndrome, is characterized by an (1) absent or hypoplastic adenohypophysis, (2) ectopic neurohypophysis, and (3) absent or hypoplastic pituitary stalk.
There are two proposed hypotheses for PSIS. The first one proposes that PSIS is an acquired injury caused by neonatal hypoxia, since there is a high association of PSIS with breech presentation and cesarean section delivery. This unexplained high incidence of breech deliveries associated with PSIS patients supports the traumatic hypothesis. However, high frequency of associated CNS malformations, such as coloboma, microcephaly, Arnold Chiari, microophthalmia, septooptic dysplasia, and corpus colossal agenesis, argues against a traumatic hypothesis. The alternative explanation is that there is failure of normal inductive events of the rostromedial neural fold during pituitary gland organogenesis and the high incidence of breech presentation can be explained by in utero hypotonia due to hormonal deficiency.
Clinically, presentation will depend on the extent of the hormonal deficiencies. Neonatal patients usually present with hypoglycemic seizure. Pediatric patients with isolated growth hormone deficiency present with variable delay in growth, while those with greater degree of hypoplasia of the pituitary stalk and anterior pituitary gland present with symptoms associated with panhypopituitarism early in life. Clinical suspicion of this syndrome is based on laboratory tests of low GH level, cortisol level, abnormal GH stimulation test, low FSH, LH, TSH and free T4. There is a high incidence of microphallus and cryptoorchidism in PSIS patients, which can be explained by the low levels of gonadotropins.
There is a male predominance with a male:female ratio of 3:1.
Imaging findings include an absent or hypoplastic anterior pituitary gland, most conspicuously seen on sagittal T1 or T2 weighted images. The pituitary infundibulum is either absent or truncated. In addition, the bright spot of the posterior pituitary gland, seen on T1 weighted sequence, is ectopic in location. The brightness of the posterior lobe does not change on a fat-suppression T1-weighted image.
Treatment consists of hormonal replacement.